The effect of sizing on the hydrodynamic parameters of the medtronic freestyle valve in vitro

Background. An in vitro model has been established to investigate the effect of sizing on the hydrodynamic characteristics and leaflet motion of the Medtronic Freestyle valve. Methods. The valves were tested in fresh porcine aortic roots. Two or three different sizes of valves were implanted in the same aortic root one after the other. The compliance of the fresh aortic and the composite roots was measured in the pressure range of 0 to 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and degree of regurgitation were measured and the effective orifice area and performance index were calculated. Leaflet motion was recorded on video. Results. The fresh aortic roots dilated by average 39.4% as the hydrostatic pressure rose from 0 to 120 mm Hg. Implantation of the Medtronic Freestyle valve did not change the distensibility of the aortic root significantly. The sizing protocol did not affect significantly the hydrodynamic performance. However, a significantly lower open leaflet bending deformation was found in the undersized valves. Regurgitation was found only at 2-mm undersized valves. Conclusions. Leaflet motion of the Medtronic Freestyle valve in vitro was best if 1 mm undersized, and this may be beneficial to long-term durability.